Attitude (Flight) Indicator

[Magician]

Has anyone found the correct procedure for uncaging the AI during a cold start that consistently results in a properly aligned AI at Takeoff?

 

I cannot find any information on how and under what conditions it is supposed to be uncaged, and regardless of what I try, the results are remarkably inconsistent. One time I glanced at it and found it aligned properly when I was getting ready for take off on the runway, other times after several minutes of level flight I've noticed it indicating properly (I tend to ignore it since it is so inconsistent.) But lately it never seems to align correctly.

 

Is there some proper way to do it? Or is it just bugged?

 

I even tried waiting motionless on the ground for 5 minutes with the suction in the green (Like it says to do for the Su-25T), but if anything, that just makes it worse.

 

Hard to believe it could be bugged that badly when it works perfectly well with a hot start mission.

Edited June 24, 2014 by Magician

[lesnyborsuk]

I would also like to know when it should be uncaged and how to set it (according to procedures).

 

I don't think you should wait so long to align it since AFAIK this is simple gyro instrument.

I have noticed that it is very capable of getting errors if you lower your RPM even for a while letting suction to go "below green".

[Magician]

I would also like to know when it should be uncaged and how to set it (according to procedures).

 

I don't think you should wait so long to align it since AFAIK this is simple gyro instrument.

I have noticed that it is very capable of getting errors if you lower your RPM even for a while letting suction to go "below green".

 

Well I found an old WWII checklist for the P-51D, It seems to have been copied word for word for the DCS Manual, except, curiously, the part about uncaging the Flight Indicator and DG, before starting the engine. That's when it is supposed to be done. It doesn't say anything further about it.

 

I went ahead and followed that procedure, including the mag tests and prop test at 2300 rpm. Taxied to the runway, and when I got lined up and brought the engine up to 30 inches with the brakes on, I noticed the Flight indicator horizon starting to move into the proper position, so I held it there and it aligned properly after about 20-30 seconds.

 

Sadly, I could not repeat that result. One thing I had remembered though, was the plane got away from me on a sharp turn with the tail wheel unlocked and I did a full 360.. I thought maybe that had something to do with it, but again, no dice with an intentional 360.

[Captain Orso]

I'm going to bump this, because I'm getting pretty strange results with the Flight Indicator's Artificial Horizon. The AH it always drifting off further and further, especially if I do a slow 360° turn in one direction. I've had it almost completely outside the window after returning to straight and level flight.

 

I haven't noticed the Angle of Bank Indicator is becoming uncalibrated.

 

I've uncaged the FI after starting the engine with the Suction Gauge at nearly green during run-up, sometimes right on the runway directly before accelerating to to take-off and sometimes after going into level flight and having trimmed the plane to stable, level flight. But the results are always the same, it's always drifting off.

 

Is anybody else (still) experiencing this issue?

[sobek]

This is not a bug, in fact this is carefully recreated behaviour of the real thing.

Edited March 14, 2015 by sobek

[Tumbleweed]

Yes indeed this is the true behavior of the AI.

 

I don't fly night missions or anything so I seldom bother with it.

The only use I find for it is when climbing through the clouds and it's easy to become disorientated or for the aircraft to go out of trim and you have nothing as a visual reference to correct against such as the horizon line.

 

Bascially I uncage mine on the runway prior to take off and forget about it.

Then when I'm doing a controled climb to my desired cruising altitude and as I get near the cloud base, I'll level the aircraft out in all aspects using the climb indicator and aproximate the bank angle with the horizon line and I'll reset the AI which I'll use to ensure I'm not inadvertently banking during the time I have zero vis as I climb through the clouds.

It's by no means accurate but it will tell you if you're banking into a nose dive while you have nothing as a visual reference point.

 

Then I don't bother with it. Rarely even look at it. Just use my eyes and other instruments to work out what's going on. Mostly temp and pressure guages so I don't pop the power plant.

 

I don't think the P-51s were designed with night fighting in mind (though I may be wrong) hence the lack of accuracy / drift in the AI which I assume pilots would correct for on route using their eyes and other insturments as reference during the day where the landscape etc can easily be observed?

 

Just my guess. I'm not a big reader of manuals so I tend to figure stuff out for myself and refer to manuals when I need to.

Edited March 15, 2015 by Tumbleweed

[Captain Orso]

I read somewhere in the forum--sorry, I can't quote the source ATM--that the deviation the Attitude (Flight) Indicator takes on, caused by flying long--in time--turns, is a few degrees (2-3). But what I've seen is much larger. Oh, well, maybe it's just my lousy flight skills.

[sobek]

The AI tends to align itself with the force vector. If you're flying 30° bank angle *coordinated* turns for long enough, you'll have a 30° bank angle offset error.

[Captain Orso]

Yes, I understand that. The question is not whether it occurs, but at what rate it occurs.

 

As I said, I read through the forum and found post from members stating that they are RL pilots, one I believe was actually an instructor, and their claim was that the change is well known, but that the rate of change is much, much smaller than what has been reported numerous times.

 

I know this doesn't mean much. It could be that everything they've said is absolutely true, but only with regards to modern AI equipment. Maybe the AI instruments were much better designed already 20 years after the war. As long as no statements were made by pilots flying with the actual equipment being simulated, it is all just speculation at the best.

 

<oppinion>*danger*danger* I rather have the feeling that if the Attitude (Flight) Indicator actually went off be 10-20° after a few normal turns the pilots of the era would have raised a ruckus about this. Who knows. Maybe they did. Maybe they were told that this is the way the equipment works and to deal with it. I'm just speculating. And as we all know, speculations are like armpits. Everybody has two or so :smilewink:</oppinion>

[Art-J]

^ I remember these posts and the question is indeed valid. It's cool that the drift is modeled, but maybe the effect is a bit excessive? Especially considering the fact that AIs in 109 and 190 don't seem to be affected by it (at least not to similar degree)...